The strength of GPS satellite signals are 15-30 dB weaker when received from geosynchronous orbit (GEO) altitudes than when viewed from low earth orbit (LEO) altitudes or from the surface of the Earth. It is well known that the time it takes to detect a spread spectrum signal is inversely proportional to the received signal power. The use of a GPS receiver on satellites at GEO altitudes is becoming main-stream. The GPS information is used to determine precise time, position, and velocity for a variety of commercial and government satellites. Traditional multi-channel receivers acquire GPS satellite signals by searching the two-dimensional code-phase and Doppler uncertainty region sequentially. At LEO altitudes, it may take such multi-channel receivers over 30 minutes to acquire GPS satellites. At GEO altitudes, the acquisition of GPS satellite signals can take hours when using traditional GPS receiver architectures due to the significantly weaker strength of the GPS satellite signals, the greatly increased search time to trigger detection, and the small number of correlators (i.e., channels) used to execute the search. Such traditional multi-channel receivers have only 12 correlators (channels) to conduct such a search.
Others have attempted to address this issue. For example, U.S. Pat. No. 7,548,199 discloses a frequency domain search function for space GPS applications. U.S. Pat. No. 6,775,319 (the '319 patent) discloses a time-domain search and tracking processor that searches different Doppler space for each satellite. The '319 patent segments the code phase into unequal segment lengths and processes each segment completely before collecting the next segment. U.S. Pat. No. 6,289,041 discloses a second series of weighted coefficients corresponding to a carrier frequency sequence for each channel. Finally, U.S. Pat. No. 4,426,712 discloses a variable frequency shifting means for shifting the frequency of stored code sequences.
As prior art systems and methods take a significant amount of time to acquire GPS satellite systems at GEO altitudes, it is desirable to provide a system and a method that could permit a more rapid acquisition of GPS satellite signals from platforms located in GEO than is possible using prior art systems and methods. Additionally, it would be desirable to provide a system and method that could permit the acquisition of GPS satellite signals from platforms located in geosynchronous orbit in approximately five minutes or less. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.